This invention relates to magnetostrictive materials and more particularly to rare earth iron magnetostrictive materials.
While conventional magnetostrictive materials--such as nickel, cobalt, iron, and alloys of these metals--have magnetostrictions at room temperature (which is the operating temperature of most transducer devices) which enable them to be used in transducer devices, it has always been desirable to obtain other magnetostrictive materials which have greater magnetostriction then those presently in use.
In 1963, it was discovered by A. E. Clark, R. Bozorth, and B. DeSavage, Phys. Letters 5, 100 (1963), that certain heavy rare earth elements have magnetostrictions about 1000 times greater than Fe and about 200 times greater than Ni. However, these enormous magnetostrictions are only present at cryogenic temperatures and are most pronounced in the neighborhood of absolute zero. At room temperature, the rare earth elements have little magnetostriction since their magnetic ordering temperatures fall below room temperature. Therefore, all are far inferior to iron, nickel, cobalt, and their alloys.
A search for materials with high magnetostriction at room temperatures was started. Highly magnetostrictive rare earths, such as Tb and Dy, were combined with the magnetic transition metals: iron, cobalt, and nickel. Of all the known rare earthtransition metal compounds, the iron compounds were found to have the largest magnetostriction at room temperature.
The usefulness of these prior art rare earth-iron materials in magnetostrictive devices (e.g., transducers, delay lines, oscillators) is limited at low magnetic fields because the crystallites of which the material is composed have a random distribution of principal axes. Because the magnetostriction is anisotropic, large inhomogenous strains are developed in the material as the temperature is lowered below the Curie point. The large inhomogenous strains hinder domain wall movement. Since domain wall motion is necessary to achieve transduction, the random polycrystals do not achieve the efficiency and dynamic range possible from rare-earth iron materials.